Spirit levels, also called bubble levels, are well known instruments used for setting horizontal or vertical surfaces. The level includes a sealed vial containing an air bubble floating in a liquid. The spirit level has a level face which is placed against the surface to set or plumbed. The particular surface is considered horizontal or vertical when the air bubble rests between predetermined graduated marks in the vial.
In general in the prior art, one single spirit level is dedicated to setting or plumbing a horizontal surface, a vertical surface and perhaps a surface tilted 45.degree. from the vertical. In certain applications, however, it is important to obtain a slightly non-horizontal or non-vertical surface. For example, in setting drainage or sewage pipes, the pipe must be tilted a few degrees from the horizontal in order to ensure proper drainage. Prior art spirit levels are inadequate for setting such surfaces. The proper angle is usually set by rough estimation with a spirit level meant for setting horizontal surfaces, or if accuracy is required, is set with specially made equipment.